Archival data protection
First Claim
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1. In a storage system having a plurality of separate storage units, a data protection system for preventing the loss of more data in one of the units than is correctable by an error correction and detection scheme to protect the data in each of the units, comprising:
- a check unit containing check bits for a plurality of the storage units on a bit position by bit position basis wherein each of said check bits is the Exclusive OR summation of the bits of a single bit position in all the storage units in the plurality of storage units;
update means including two read before write station means that read the data in a bit position of a separate one of the storage units and the check unit before writing data in the same bit position for updating check bits of the check unit each time a bit in one of the plurality of storage units is changed said update means including means in one of said read before write stations for obtaining a first Exclusive OR sum of the original and new values for any changed digit and means in said other read before write station for obtaining the Excluisve OR sum of the results of the first Exclusive OR sum and the check bit in the changed bit position to generate the updated check bit covering data in the changed bit position;
restore means including the two read before write station means that read the data in a bit position of a separate one of the storage or check units before writing data in the same bit position for exclusive ORing the data in the check unit with the data in all the storage units other than said one storage unit to reproduce data in said one storage unit when the data in said one storage unit is uncorrectable by said error correction and detection scheme whereby catastrophic losses of data are prevented.
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Abstract
This specification describes a system for preventing the catastrophic loss of data in one storage unit of a storage system comprised of a plurality of such storage units. In this system one of the plurality of storage units is used to store parity bits for the storage system, bit position by bit position. To be more specific, if the data in each of the storage units is considered to be a linear string of bits the storage unit containing the parity bits would contain a parity or Exclusive OR sum of all the first bits of all the storage units or, in a more general case, the j.sup.th bit of the check storage unit is the parity or Exclusive OR sum of all the j bits of all the storage units.
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Citations
2 Claims
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1. In a storage system having a plurality of separate storage units, a data protection system for preventing the loss of more data in one of the units than is correctable by an error correction and detection scheme to protect the data in each of the units, comprising:
- a check unit containing check bits for a plurality of the storage units on a bit position by bit position basis wherein each of said check bits is the Exclusive OR summation of the bits of a single bit position in all the storage units in the plurality of storage units;
update means including two read before write station means that read the data in a bit position of a separate one of the storage units and the check unit before writing data in the same bit position for updating check bits of the check unit each time a bit in one of the plurality of storage units is changed said update means including means in one of said read before write stations for obtaining a first Exclusive OR sum of the original and new values for any changed digit and means in said other read before write station for obtaining the Excluisve OR sum of the results of the first Exclusive OR sum and the check bit in the changed bit position to generate the updated check bit covering data in the changed bit position;
restore means including the two read before write station means that read the data in a bit position of a separate one of the storage or check units before writing data in the same bit position for exclusive ORing the data in the check unit with the data in all the storage units other than said one storage unit to reproduce data in said one storage unit when the data in said one storage unit is uncorrectable by said error correction and detection scheme whereby catastrophic losses of data are prevented.
- a check unit containing check bits for a plurality of the storage units on a bit position by bit position basis wherein each of said check bits is the Exclusive OR summation of the bits of a single bit position in all the storage units in the plurality of storage units;
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2. The storage system of claim 1 wherein said restore means includes:
- means at one of said stations for reading the data out of each of the storage units not containing a catastrophic loss and the check unit to produce a restore output; and
means at the other of the stations for Exclusive ORing said restore output with a new storage unit containing all binary zeros to reproduce the destroyed data.
- means at one of said stations for reading the data out of each of the storage units not containing a catastrophic loss and the check unit to produce a restore output; and
Specification
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Current AssigneeArvind M. Patel, Douglas C. Bossen, Mu-Yue Hsiao
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Original AssigneeArvind M. Patel, Douglas C. Bossen, Mu-Yue Hsiao
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InventorsPatel, Arvind M., Bossen, Douglas C., Hsiao, Mu-Yue
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Primary Examiner(s)Atkinson, Charles E.
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Assistant Examiner(s)Dildine, Jr., R. Stephen
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Application NumberUS05/366,936Time in Patent Office673 DaysField of Search235/153AM 340/146.1AG,146.1F,174ED,174.1B,174.1R,176.1AL 360/53US Class Current714/805CPC Class CodesG06F 11/1008 in individual solid state d...G06F 11/1076 Parity data used in redunda...
